1. Field of the Invention
The present invention relates to a method of forming barrier ribs of a display panel, particularly a method of forming barrier ribs of a display panel such as a plasma display panel (PDP), a plasma addressing liquid crystal panel and a field emission display panel, which includes barrier ribs for providing partitions for pixels and maintaining a spacing between a front substrate and a rear substrate.
2. Description of Related Arts
These kinds of display panels are used in various fields. The PDP, in particular, is suitable for a high-vision display since it exhibits an excellent visibility and a high display speed. The PDP has been attracting considerable attention in recent years.
The PDP is a self-luminous display panel having a discharge space defined between a pair of substrates with electrodes arranged in a matrix therein. The pair of substrates are spaced at a minute distance in an opposing relation and the peripheries thereof are sealed together.
The PDP using a matrix display system are provided with barrier ribs having a height of about 100 .mu.m to about 200 .mu.m for partitioning the discharge space. For example, a PDP of a surface discharge type suitable for fluorescent color display includes linear barrier ribs equidistantly arranged across lines for display. The distant between adjacent barrier ribs is, for example, about 200 .mu.m for a 21-inch color PDP. The barrier ribs prevent discharge coupling and color cross-talk between adjacent cells.
Known methods of forming the barrier ribs include a screen printing method, a sandblast method and a hydro-honing method.
In the screen printing method, a pattern of a barrier rib configuration is repeatedly printed ten-odd times to form the barrier ribs. The screen printing method has the advantage of making the most of materials and reducing production costs. However, there arise problems in screen production accuracy, repeated printing accuracy and durability of the screen when barrier ribs are to be formed over a large-sized display panel exceeding 40 inches or when barrier ribs having a minute width are to be arranged at a very small distance for a small-sized high-definition display panel.
In the sandblast method, fine cutting particles are carried on a flow of air and jetted onto a layer of a barrier-rib material with a cutting mask pattern formed thereon before hand, to cut a portion that is not covered with the cutting mask pattern to form barrier ribs. The sandblast method has problems of wastes of the barrier-rib material removed by cutting and increasing costs due to a necessary photolithography. However, the sandblast method has the advantage of achieving a higher accuracy over the screen printing method.
In the hydro-honing method, liquid such as water is jetted for cutting. The hydro-honing method is almost the same as the aforesaid sandblast method in process and possesses a similar advantage thereto.
The sandblast and hydro-honing methods are often used for forming barrier ribs for a large-sized display panel or a small-sized high-definition display panel because these methods are suitable for attaining a high accuracy.
An exemplary prior art formation of barrier ribs using the sandblast method is explained for a color PDP, particularly an AC-driven PDP of the surface discharge type.
FIGS. 14A to 14D illustrate the formation of barrier ribs for a PDP using the sandblast method. As shown in the figures, the barrier ribs are formed by the following processes:
A base layer, an address electrode and an insulating layer are formed on a rear glass substrate 21 (the base layer, address electrode and insulating layer are not shown). A layer of a barrier rib material 51 is formed in a desired thickness over the insulating layer (see FIG. 14A). As the barrier rib material, used is a glass paste containing a glass powder and resin components as a filler and a binder. The barrier rib material layer 51 is dried and a mask pattern 54 of a barrier rib configuration is formed on the barrier rib material layer 51 by photolithography (see FIG. 14B). A cutting medium is jetted thereon by a sandblaster 70 to cut a portion of the barrier rib material layer 51 that is not covered with the mask pattern 54. The barrier rib material layer is thus formed into a cut barrier rib layer corresponding to barrier ribs (see FIG. 14C). The mask pattern 54 is peeled off and then the cut barrier rib layer is sintered into glass barrier ribs 29 (see FIG. 14D).
In the field emission display panel and in a monochromatic PDP having a large dot pitch, glass beads having a diameter of several hundred .mu.m are generally provided as spacers between the front and rear substrates to ensure the spacing therebetween. In this case, pixels do not necessarily need to be separated by partitions. It is enough to ensure the spacing between the front and rear substrates. However, barrier ribs similar to those of the plasma display, if used, enhances the visibility. For this reason, the barrier ribs are sometimes formed for the field emission display panel and the monochromatic PDP.
The above described sandblast method is a useful method for forming the barrier ribs for a plane display panel. However, when the barrier rib material layer is cut by the sandblast method, especially as the width of the barrier ribs is reduced, adhesion between the mask pattern and the barrier rib material layer drops. Sometimes the mask pattern peels off from the barrier rib material layer during cutting.
To ensure a close adhesion between the mask pattern and the barrier rib material layer, the amount of the binder component in the barrier rib material may be increased. However, the increase in the amount of the binder component causes a decline in a cutting rate, and the decline in the cutting rate gives rise to a further need to strengthen the adhesion between the mask pattern and the barrier rib material layer.
To solve this problem, it is necessary to improve the adhesion without reducing the cutting rate. Japanese Unexamined Patent Publication No.Hei 7(1995)-161298 proposes a solution therefor. In a proposed method, the amount of the binder component in the barrier rib material is not changed, but on this barrier rib material layer, a second barrier rib material layer is formed which contains an increased amount of the binder component. According to this method, the adhesion between the mask pattern and the barrier rib material layer is expected to be strengthened to some extent without significantly reducing the cutting rate of the sandblasting. However, when the barrier ribs are to be arranged at a more minute distance for securing a display panel of higher-definition, the width of the barrier rib must also be reduced. Accordingly, the adhesion between the mask pattern and the barrier rib layer needs to be further strengthened.
As an alternative solution, a top surface of the barrier rib material layer may be roughened. However, the top surface of the barrier ribs is desired to be as flat as possible since the barrier ribs are formed for prohibiting discharge coupling between the partitions. If the barrier ribs have a rough top surface, they do not contact the front substrate closely when the front and rear substrates are assembled into a display panel. This results in gaps between the barrier ribs and the front substrate which allow discharge coupling. As a result, the quality of the display panel is debased.
Additionally, Japanese Unexamined Patent Publication No. Hei 4(1992)-95328 discloses a method for flattening the top surface of the barrier ribs.